Battery problem with 96 Ford Ranger XLT

I bought my truck a couple a weeks ago, and the lady said the battery was almost brand new. I drove it a few times, and my dad used the battery to jump his work truck. Also I have been listenin to the stereo alot with the car off, and just the key turned so the i can turn the radio on. All of a sudden when i get into my car and try to turn it on or anything it will go on, and then a few seconds later just dye. It is very dim inside. Do I just need to charge the battery, or get a whole new one?

thanx

could be a defect battery, also could be a defect cable. does it jump start with no problems?

yea. It just needed to be charged. It works fine now. Thanx. I just have one more question. There is not that much to put speakers in my truck, besides behind the seats. IT is only a 2 door. What kind of speakers do you reccomend, and also what face plate with the speakers?

Thankx